The increasing demand to improve vehicular fuel economy and reduce vehicular emissions has led to the development of both hybrid vehicles and pure electric vehicles. Pure electric vehicles may be powered by a battery pack (which is made up of numerous smaller modules or cells), while hybrid vehicles include two or more energy sources, such as a gasoline (also referred to as an internal combustion) engine used as either a backup to or in cooperation with a battery pack. There are two broad versions of hybrid vehicles currently in use. In a first version (known as a charge-depleting hybrid architecture), the battery can be charged off a conventional electrical grid such as a 120 VAC or 240 VAC power line. In a second version (known as a charge-sustaining hybrid architecture), the battery receives all of its electrical charging from one or both of the internal combustion engine and regenerative braking. In either configuration, various parameters associated with the battery pack can be monitored to ensure proper operation.
One such parameter that is useful in monitoring the proper operation of a battery pack (or battery) is the temperature of a cell in the battery pack. One method of determining the temperature of a cell in a battery pack is to put a sensor in the core of the cell; this method has proven to be expensive and unreliable. Another method involves directly measuring the temperature of the surface of the cell with a sensor. However, the temperature of the surface of a cell in a battery pack is often different from the temperature of the core of a cell in a battery pack, in some instances as large as 30° C. These and other problems make it difficult to accurately and reliably estimate the core temperature of a battery pack.